Build a demo mobile app, preferrably Xamarin

Simple demo mobile application, as a POC which will evolve later. Login page against OAuth service, which I will provide. If logged in user role is admin, he will be able to post some dummy text data against a web service, and send push notifications. Users will receive these push notifications, opening page within the mobile app with link to show posted dummy data. demo preferably in Xamarin, working on both ios and android Full source code will be delivered